Previous attempts to incorporate the body of a vehicle as an antenna have proven ineffective. Because of the unusual characteristics and difficult problems encountered in extracting usable radio frequency (RF) signals from such conductive structures, the state of the art has developed slowly.
A number of patents have been issued in this field, but none of the techniques taught in the prior art are similar to those disclosed in the present invention, nor have the earlier inventions worked well in practice.
U.S. Pat. No. 3,717,876 to Volkers, "Ferrite Antenna Coupled to Radio Frequency Currents in Vehicle Body," describes a cascade arrangement wherein a Faraday cage acts as the primary antenna, which intercepts the electromagnetic waves and reradiates them to a secondary antenna with in the Faraday cage. In one of such arrangements, the body of an automobile is used as the Faraday cage while a ferrite antenna is used as the secondary antenna.
U.S. Pat. No. 3,916,413 to Davis, "Remotely Tuned Conductive-Boay Antenna system," discloses a voltage and impedance transformer applied to increase the inductive reactive of coupling to the vehicle body. Such coupling is achieved by using the magnetic signal from the fine wire antenna in the windshield/window or a whip antenna on most automobiles.
U.S. Pat. No. 3,961,330 to Davis, "Antenna System Utilizing Currents in Conductive Body," an improvement over the aforementioned antenna system to the same inventor, includes coupling at locations such as a vertical column of the vehicle where the conductive body has reduced cross section.
U.S. Pat. No. 4,100,546 to Campbell, "Airborne Antenna System Employing the Airframe As An Antenna," teaches a phase front homing system airborne antenna array employing portions or the vertical landing gear struts as antenna elements. This system obtains the desired homing direction by measuring the phase difference between signals picked up by the two antenna elements.
Finally, U.S. Pat. No. 4,117,490 to Arold et al, "Inconspicuous Antenna System Employing the Airframe As An Antenna," also discloses a phase front homing system airborne antenna array application, which is improved by inclusion of discrete axial coupling sleeves in the landing struts.
The inventor is unaware of applications utilizing the novel arrangements more fully described below, nor applications wherein the above-described prior art has been successfully implemented. Inventor's empirical data, on the other hand, demonstrate the efficacy of the instant invention.